A key component of two-way optical transmission systems is the transmitter-receiver (Tx/Rx) package. Such packages are currently fabricated with 1.times.2 or 2.times.2 couplers in combination with standard transmitters, such as laser diodes or in some applications, light emitting diodes, and standard receivers, such as PIN diodes. The couplers of these systems are generally of two types:
(a) Wavelength Division Multiplexing (WDM) couplers, utilized in two-wavelength systems generally as combiners, splitters and filters, or
(b) 3 dB splitters employed in single wavelength transmission systems.
One of the drawbacks with using 3 dB splitters is the 3 dB power loss in both transmitted and received power.
Three embodiments of the standard coupler are currently commercially available. First, the fused biconically tapered fiber coupler is fabricated by fusing two fibers together and then drawing them to a smaller diameter to cause coupling. Second, the multiclad coupler is fabricated by placing two fibers in a tube and heating and drawing the tube and fibers to induce coupling. Third, planar devices, including geometrically split or coupled waveguide paths, are formed by ion exchange in glass or other photolithographic techniques.
The first and second embodiments have integral fiber pigtails for attachment to the transmitter and receiver, making integration into small, robust packages difficult. The aforementioned third embodiment typically includes fiber pigtails attached to the planar substrate. Some designs have been proposed for directly coupling the Tx and Rx to the planar substrate without intermediate pigtails. Such designs require only a pigtail for attachment to the optical fiber transmission link.
The subject invention replaces the standard couplers with coaxial couplers for the purpose of achieving compact coupling devices without pigtails between the coupler and the Tx or Rx. The present invention makes possible the fabrication of a compact Tx/Rx package. Further, one embodiment of this invention provides for a short fiber extension which can be aligned to a transmitter similar to current techniques for fiber-transmitter alignment in current Tx/Rx designs. Coaxial coupling also provides flexibility in design. The invention provides more facile transmitter-receiver separation as well as the integration of source-fiber lens configurations for improved coupling efficiency. Also, the invention makes possible greater options in connecting devices into the system, which improves the flexibility in overall system design.